Cemented carbides are widely utilized in a broad range of applications today. For example, cemented carbides are utilized in cutting tools, mining tools and wear parts. Accordingly, a huge amount of discarded cemented carbide bodies is produced every year.
For economic reasons the ability to recycle/recover cemented carbides from discarded or unused cemented carbide bodies, i.e. cemented carbide scrap, is of great interest since the raw materials used in production of new cemented carbide bodies are expensive. Furthermore, the ability to recycle cemented carbides is also of great interest for environmental reasons. The use of recycled material in production of new cemented carbide bodies reduces the energy consumption and the environmental impact significantly as compared to the use of virgin raw materials.
Recycling/recovery of cemented carbides from discarded or unused cemented carbide bodies may be performed by degradation to powder by chemical, metallurgical or mechanical processes. Commonly utilized processes for recycling of cemented carbides by degradation to powder are, for example, the “cold stream process” and the “zinc process”. The “cold stream process” provides a mechanical disintegration of cemented carbide bodies to powders of hard constituents and binder metals. The “zinc process” is characterized by a transformation of cemented carbide bodies to powder by metallurgical means. In the “zinc process” the cemented carbide bodies are immersed into molten zinc in an electrical furnace. Zinc is then brought to diffuse into the cemented carbide and to alloy itself with the binder metal, usually cobalt. Thereby the cemented carbide disintegrates into powder. The zinc is then distilled at a certain temperature and is thus removed from the furnace, whereby the remaining powder comprises WC and the binder metal separated from each other. The “zinc process” is described in, for example, U.S. Pat. No. 3,595,484.
During recent years the amount of utilized recycled material in production of new cemented carbide bodies has increased. However, as a result the purity requirements of the recycled material have also increased, i.e. the allowable proportion of undesired material remaining in the recycled material has been lowered.
Usually, collections of discarded or unused bodies, such as cutting tools, mining tools, wear parts, etc., to be introduced into a process for recycling of cemented carbides include not only bodies of cemented carbide but also non-cemented carbide bodies, i.e. bodies of other materials such as e.g. cermets, ceramics and steel. However, non-cemented carbide bodies often include elements and/or compounds that are undesired in recycled material to be used for production of new cemented carbide bodies. Thus, non-cemented carbide bodies that are present in a collection of bodies introduced into a process for recycling of cemented carbides can make the obtained recycled material unsuitable as raw material for production of new cemented carbide bodies.
Many cermet materials have a high content of nitrogen. The nitrogen originating from cermet bodies is not removed during a recycling process for recycling of cemented carbides. Thus, in case cermet bodies are present in a collection of bodies introduced into a process for recycling of cemented carbides, nitrogen will be present in the obtained recycled material. A too high degree of nitrogen in the recycled material can form an undesirable concentration gradient of the gamma phase during sintering when the recycled material is utilized in production of new cemented carbide bodies. Such a gradient is not desired in all cemented carbide grades.
Furthermore, many cermet materials also contain other elements and/or compounds that make the recycled material unsuitable as raw material for the manufacture of at least certain cemented carbide grades. For example, many cermet materials include nickel and/or titanium. These elements are commonly used as property enhancing additions in a variety of cemented carbide grades. However, for certain other grades these elements are unwanted or even detrimental to the properties.
In addition, ceramic materials and steel materials include elements and/or compounds that may make the obtained recycled material unsuitable as raw material for the manufacture of at least certain cemented carbide grades.
Thus, in order to fulfill the purity requirements of recycled cemented carbide materials, there is a need to separate non-cemented carbide bodies, in particular cermet bodies, from a collection of bodies, which is intended to be introduced into a process for recycling of cemented carbides, before start of the recycling process. In addition, there is a need to perform the separation in a simple and cost-effective way.